u-boot/board/scb9328/lowlevel_init.S

/*
 * Copyright (C) 2004 Sascha Hauer, Synertronixx GmbH
 *
 * SPDX-License-Identifier:	GPL-2.0+
 */

#include <config.h>
#include <version.h>
#include <asm/arch/imx-regs.h>

.globl lowlevel_init
lowlevel_init:

	mov	r10, lr

/* Change PERCLK1DIV to 14 ie 14+1 */
	ldr		r0,	=PCDR
	ldr		r1,	=CONFIG_SYS_PCDR_VAL
	str		r1,   [r0]

/* set MCU PLL Control Register 0 */

	ldr		r0,	=MPCTL0
	ldr		r1,	=CONFIG_SYS_MPCTL0_VAL
	str		r1,   [r0]

/* set mpll restart bit */
	ldr		r0, =CSCR
	ldr		r1, [r0]
	orr		r1,r1,#(1<<21)
	str		r1, [r0]

	mov		r2,#0x10
1:
	mov		r3,#0x2000
2:
	subs	r3,r3,#1
	bne		2b

	subs	r2,r2,#1
	bne		1b

/* set System PLL Control Register 0 */

	ldr		r0,	=SPCTL0
	ldr		r1,	=CONFIG_SYS_SPCTL0_VAL
	str		r1,   [r0]

/* set spll restart bit */
	ldr		r0, =CSCR
	ldr		r1, [r0]
	orr		r1,r1,#(1<<22)
	str		r1, [r0]

	mov		r2,#0x10
1:
	mov		r3,#0x2000
2:
	subs	r3,r3,#1
	bne		2b

	subs	r2,r2,#1
	bne		1b

	ldr		r0,   =CSCR
	ldr		r1,   =CONFIG_SYS_CSCR_VAL
	str		r1,   [r0]

/* I have now read the ARM920 DataSheet back-to-Back, and have stumbled upon
 *this.....
 *
 * It would appear that from a Cold-Boot the ARM920T enters "FastBus" mode CP15
 * register 1, this stops it using the output of the PLL and thus runs at the
 * slow rate. Unless you place the Core into "Asynch" mode, the CPU will never
 * use the value set in the CM_OSC registers...regardless of what you set it
 * too!  Thus, although i thought i was running at 140MHz, i'm actually running
 * at 40!..

 * Slapping this into my bootloader does the trick...

 * MRC p15,0,r0,c1,c0,0    ; read core configuration register
 * ORR r0,r0,#0xC0000000   ; set asynchronous clocks and not fastbus mode
 * MCR p15,0,r0,c1,c0,0    ; write modified value to core configuration
 * register
 */
	MRC p15,0,r0,c1,c0,0
	ORR r0,r0,#0xC0000000
	MCR p15,0,r0,c1,c0,0

	ldr		r0,	=GPR(0)
	ldr		r1,	=CONFIG_SYS_GPR_A_VAL
	str		r1,   [r0]

	ldr		r0,	=GIUS(0)
	ldr		r1,	=CONFIG_SYS_GIUS_A_VAL
	str		r1,   [r0]

/* CS3 becomes CS3 by clearing reset default bit 1 in FMCR */

	ldr		r0,	=FMCR
	ldr		r1,	=CONFIG_SYS_FMCR_VAL
	str		r1,   [r0]

	ldr		r0,	=CS0U
	ldr		r1,	=CONFIG_SYS_CS0U_VAL
	str		r1,   [r0]

	ldr		r0,	=CS0L
	ldr		r1,	=CONFIG_SYS_CS0L_VAL
	str		r1,   [r0]

	ldr		r0,	=CS1U
	ldr		r1,	=CONFIG_SYS_CS1U_VAL
	str		r1,   [r0]

	ldr		r0,	=CS1L
	ldr		r1,	=CONFIG_SYS_CS1L_VAL
	str		r1,   [r0]

	ldr		r0,	=CS2U
	ldr		r1,	=CONFIG_SYS_CS2U_VAL
	str		r1,   [r0]

	ldr		r0,	=CS2L
	ldr		r1,	=CONFIG_SYS_CS2L_VAL
	str		r1,   [r0]

	ldr		r0,	=CS3U
	ldr		r1,	=CONFIG_SYS_CS3U_VAL
	str		r1,   [r0]

	ldr		r0,	=CS3L
	ldr		r1,	=CONFIG_SYS_CS3L_VAL
	str		r1,   [r0]

	ldr		r0,	=CS4U
	ldr		r1,	=CONFIG_SYS_CS4U_VAL
	str		r1,   [r0]

	ldr		r0,	=CS4L
	ldr		r1,	=CONFIG_SYS_CS4L_VAL
	str		r1,   [r0]

	ldr		r0,	=CS5U
	ldr		r1,	=CONFIG_SYS_CS5U_VAL
	str		r1,   [r0]

	ldr		r0,	=CS5L
	ldr		r1,	=CONFIG_SYS_CS5L_VAL
	str		r1,   [r0]

/* SDRAM Setup */

	ldr		r0, =SDCTL0
	ldr		r1, =PRECHARGE_CMD
	str		r1,   [r0]

	ldr		r0, =0x08200000
	ldr		r1, =0x0 /* Issue Precharge all Command */
	str		r1,   [r0]

	ldr		r0, =SDCTL0
	ldr		r1, =AUTOREFRESH_CMD
	str		r1,   [r0]

	ldr		r0, =0x08000000
	ldr		r1, =0x0 /* Issue AutoRefresh Command */
	str		r1,   [r0]
	str		r1,   [r0]
	str		r1,   [r0]
	str		r1,   [r0]
	str		r1,   [r0]
	str		r1,   [r0]
	str		r1,   [r0]
	str		r1,   [r0]

	ldr		r0, =SDCTL0
	ldr		r1, =0xb10a8300
	str		r1,   [r0]

	ldr		r0, =0x08223000 /* CAS Latency 2 */
	ldr		r1, =0x0   /* Issue Mode Register Command, Burst Length = 8 */
	str		r1,   [r0]

	ldr		r0, =SDCTL0
	ldr		r1, =0x810a8200 /* Set to Normal Mode CAS 2 */
	str		r1,   [r0]

	mov	pc,r10